Plugging a speaker port

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So the BW PM1 come with little foam ports, it is well diagramed in the manual that plugging ports cause attenuation of bass. Does plugging the ports also affect efficiency of a speaker? Like if the standard efficiency is 87db/w, does it dip even further with a sealed enclosure?
Magico, JL, Emm, ARC Ref 10 line, ARC Ref 10 phono, VPI, Lyra, Boulder, AQ Wel, SRA Scuttle Rack, Bluesound

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